Effect of high HCO_3~- concentrations on the growth, physiology, and biochemistry of Gracilaria tenuistipitata

LI Xiaowei,YAO Zongli,ZHOU Kai,LIN Tingting,WANG Hui,LAI Qifang,YING Chengqi East China Sea Fisheries Research Institute,Research Center for Saline-alkali Water Fisheries Technology,Chinese Academy of Fishery Sciences;Key Laboratory of East China Sea & Oceanic Fishery Resources Exploitation and Utilization,Ministry of Agriculture,Shanghai 200090,China

HCO3;Gracilaria tenuistipitata;specific growth rate;photosynthetic pigment;antioxidase;malonaldehyde content

The total amount of dissolved inorganic carbon in water includes CO2,H2CO3,HCO3-,and CO32-.At a pH of between 8.2–8.4,HCO3- is the predominant component(approximately 90%),and free CO2 contributes less than 1%.In China,saline-alkali water covers about 45.87 million ha,most of which is characterized by high carbonate alkalinity(CA) concentrations.Since high CA is a major stressor for living organisms,most of these saline-alkali water areas have little evidence of life.To take advantage of this unexploited resource,researchers have trialed the use aquatic plants to reduce the HCO3- concentration in saline-alkali waters.The seaweed Gracilaria tenuistipitata var.liui Zhang et Xia is characterized by rapid growth and easy cultivation.The objective of this study was to investigate the effects of high HCO3- concentrations on the growth,physiology,and biochemistry of G.tenuistipitata to provide basic information for the development of saline-alkali water using macroalga.G.tenuistipitata were grown for 10 d in a 250 mL Erlenmeyer flask containing 200 mL culture medium with 1.8(control),12,24,36,or 48 mmol/L HCO3-.We then compared the physiological and biochemical characteristics of G.tenuisti-thetic pigments,and led to membrane lipid peroxidation.In addition,the SGR and superoxide dismutase(SOD) and peroxidase(POD) activity increased in G.tenuistipitata as the concentration of HCO 3 increased from 1.8 to 24 mmol/L,then decreased in the range between 24 to 48 mmol/L.HCO 3 content was significantly correlated with the content of chlorophyll a(P<0.01),phycoerythrobilin,carotenoids,and malonaldehyde(P<0.05).SGR was significantly correlated with SOD activity(P<0.05),but not with the content of photosynthetic pigments,suggesting that the inhibitory effect of high HCO 3 concentration on the growth of G.tenuistipitata may damage the antioxidant system,not the photosynthetic system.With regard to the growth of G.tenuistipitata,high HCO 3 concentrations appear to be beneficial by increasing the availability of inorganic carbon for the photosynthesis.However,the tradeoff is the production of 2 3 CO which forms a CaCO 3 precipitate with Ca 2+,reduces the synthesis of photosynthetic pigments,and causes damage to the membrane system.The antioxidant defense system appeared to protect G.tenuistipitata at HCO 3 concentrations of <24 mmol/L.However,antioxidant activity(e.g.,SOD and POD) was significantly impaired at HCO 3 concentrations of >24 mmol/L,suggested the defense system was damaged.As a result,the SGR of G.tenuistipitata was lower at these concentrations.Based on our results,an HCO 3 concentration of 24 mmol/L appears optimal for the growth of G.tenuistipitata,and concentrations <24 mmol/L appear to be detrimental.